How does maintainance margin work when withdrawing money on margin?

Question

I have an account with IB and 50% maintenance margin.

The most common use of margin ist buying stocks with loaned money, for example:

You buy 100 shares for 1$ each, 50% of which is your money, the rest is margin. You owe 50$. Stock price drops by 0.2, your total value is 80$, but you still owe 50$. Now your money is 30$ and the loan is still 50$. in order to get margin called, the price needs to fall below 0.75$. At that point you still owe 50$, but only have 25$ of your own money, so this is the threshold of a margin call correct?

Now imagine a different scenario, where you don't buy stocks with margin but currency, which you then withdraw.

Specific example:

500k in stocks without margin Take out margin loan for 200k, don't buy stocks with it, but simply withdraw it.

If your 500k in stocks drops by 50%, you now have only 250k of stocks, that are yours and you owe 200k for the loan. This shouldn't resutl in a margin call correct?

Only when your initial 500k stocks drops to less than 50% of your loan (100k) do you get margin called, correct?

Answer 1

For non Pattern Day Traders, IBKR has an initial margin of 50% and a maintenance margin requirement (MMR) of 30%.

Their maintenance margin requirement is 30% of the stock value or $2,000, whichever is greater. But going with your first example, if you buy $100 worth of stock with $50, at 30%, the MMR is 10/7 times the amount of the debt or $71.43 . Below that you get a margin call.

Scenario two:

If you have $500k of stock, you withdraw $200k and the stock drops $250k, you are at 20% margin ($50k equity divided by $200k debt) and you get a margin call.

Here's a clear explanation of MMR from Schwab. See page 10.